Schizophrenia; evaluation of the dopamine hypothesis.

Question 1

Evaluation; Dopamine imbalances may be caused

Answer 1

• If dopamine imbalances are responsible for schizophrenia, the question then has to be what causes the dopamine imbalances?
• Many researchers believe that it may be a genetic predisposition, and indeed twin and family studies indicate that there is some genetic basis for schizophrenia.
• For example the classic study Irving Gottesman et al (1991) looked at incidence of schizophrenia in cousins, grandchildren, half siblings, parents, siblings, non identical and identical twins. As genetic similarity increased so did the probability of both individuals having schizophrenia.
• However research looking for one or a few candidate genes has been dissappointing.
• in 2014, the Schizophrenia Working Group of the Psychiatric Genomics Consortium (a group of over 300 scientists of over 300 scientists from 35 countries) reported that there were 108 genetic loci associated with schizophrenia. This shows that although there may indeed be a genetic basis for schizophrenia, it is a complex matter- more than just a few abnormal dopamine genes.

Question 2

Evaluation; Measuring metabolites

Answer 2

• It is not easy to make direct measurements of neurotransmitters such as dopamine, and most of the research that supports the dopamine hypothesis is based on metabolite research.
• in order to assess neurotransmitter levels we have to measure the metabolite levels (what neurotransmitters get broken down into) in cerebrospinal fluid.
• Dopamine becomes metabolised into HVA or homovallinic acid and this is measured in cerebrospinal fluid, which can only be obtained from a lumbar puncture (an unpleasant procedures).
• The participants diet and drug use may also seriously affect metabolite levels and, even when research is conducted under controlled conditions, the results can be difficult to interpret with HVA levels varying widely between participants.
• This suggests that until we have refined procedures for measuring neurotransmitters we should perhaps be cautious in the conclusions we draw from metabolite based research.

Question 3

Evaluation; The role of serotonin

Answer 3

• Dopamine is not the only neurotransmitter implicated in schizophrenia. Serotonin, another neurotransmitter, has also been identified as a potential influence.
• Conventional Antipsychotics have traditionally worked by primarily blockading the D2 receptor sites, however not all of those with schizophrenia benefit from these drugs.
• newer, atypical antipsychotics such as clozapine, block the D2 recepetor sites and also the serotonin receptor 5-HT2A. although this may not suggest that the dopamine hypothesis is completely wrong, it certainly suggests it cannot explain schizophrenia on its own. This means that, at best, it is only a partial explanation.

Question 4

Evaluation; cause or effect?

Answer 4

• although the dopamine hypothesis proposes that dopamine imbalances cause schizophrenia, it could also legitimately be proposed that schizophrenia causes the dopamine imbalances.
• Are the dopamine discrepancies seen in some people with schizophrenia just another symptom of the disease, rather than a cause of it?
• There is some hope that as investigative techniques become less invasive, we will be able to conduct research that will be able to establish which comes first, a dopamine or schizophrenia.
• research using PET scans ( e.g. Copolov and Crook 2000) hasn’t yet been able to even detect differences in the dopamine activity of the brains of individuals with schizophrenia and those without. So it may be some time before we know for certain if dopamine imbalances cause schizophrenia causes dopamine imbalances.